In a wide variety of hydraulic pumps, a positive displacement pump is one typical representative type of pump. The pump periodically transfers energy to liquid so as to pressurize the liquid thereby forcedly discharging the liquid by means of periodically changing a sealed working space volume for containing liquid. The discharged oil flow has a value depending on the change of the volume of the sealed chamber. Two requirements for work are necessary as follows: 1) the sealed volume changes periodically, wherein the oil is sucked when the sealed volume increases, and the oil is pressurized when the sealed volume decreases; 2) an oil dispensing device is provided for ensuring that the sealed volume is only in communication with an oil suction pipe when the sealed volume increases and is only in communication with an oil discharge pipe when the sealed volume decreases.
The traditional positive displacement pump generally needs to be rotated by a mover with a relatively high rotating speed. However, the traditional positive displacement pump is not applied in case of a reciprocating drive and a relatively low operating speed.